Pulse generator



p l 1943' I R. c. JENSEN 2,440,547

PULSE GENERATOR Original Filed Jan. 23, 1943 Inventor? Richard C. Jensen,

His Attorney Patented Apr. 27, 1948 Richard C. Jensen, Scotia,

Company, a corporation of General Electric New York N. Y., assignor to Original application January 23, 1943, Serial No.

473,279. Divided an 1944,,Serial No. 530,624

2 Claims. 1

Thisapplication is adivision of my application SerialNo. 473,279, filed January 23, 1943.

The present invention relates to a pulse generator for producing pulses of variable width or duration. 7

An object of my invention is to provide an improved circuit for obtaining variable width pulses.

The novel features which I believe to be characteristic of my invention are set forth with particularity in the appended claims. My invention itself, however, both as to its organization and method of operation, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawing in which the single figure is a circuit diagram of a pulse generator embodying my invention.

Referring to the drawing, there is shown a pulse generator for converting the voltage of an alternating current source from a more or less peaked wave form to square wave pulses of variable width.

The input of the pulser, which is fed from the alternating current source 5, consists ofa multivibrator having electron discharge devices 23 and 24 which may be within a single envelope. The device 23, which is normally conducting, has its anode 23a connected to the positive terminal of the power supply through resistances 25 and 25a and its cathode 23b connected to ground through resistance 26. While the device 23 is conducting, the anode voltage is less than the voltage of the power supply by the drop through the resistance 25 and 25a. The grid 21 of the device 23 is connected to the alternating voltage source 5 and is driven negatively during the peaks Zia, causing a decrease in the anode current with the resultant increase in anode voltage which is applied through a condenser 28 to the grid 29 of the tube 24.

The grid 29 has a negative bias obtained from a resistance 29a in series with a resistance 2% across a source of negative bias potential and maintains the device 24 nonconducting until the negative bias is overcome by the voltage from the anode 23a. At this point current flows through a resistance 39 to the device 24 and through the resistance 25. The voltage drop through the resistance 25 drives the grid of device 23 negative with respect to the cathode of that device, causing a rapid interruption of the current in the device 23 and a sudden increase in the current in the device 2%. This results in a sudden drop in voltage at the anode 3! of the d this application April 12,

device 24 as shown at 35. As the condenser" 28 is charged, the positive bias on the grid decreases and causes a decrease in the current in tube 25. The decreased current flowing through the resistance 25 renders the grid of device 23 positive with respect to the cathode, causing that device to become conducting, and the decrease in voltage at the anode 23a drives the grid of device 2 5 to cut-oft". The decrease in current in the device 2 is accompanied by a rise in anode voltage which, as shown at 34, is not as rapid as the drop.

The negative dip in the voltage at the anode 38 has a wave shape-determined by the regenerative build-up time of the device 26 and is independent of the wave shape of the alternating voltage supply 5, although a peaked wave shape will provide a more definite starting point.

The output voltage of the device 2 3 is fed through a diiierentiating circuit consisting of a condenser Siand a resistance 35 which causes a more sharply peaked voltage 31 to appear across the resistance 36. This peaked voltage is ap plied through a variable tap 38 to the grid 39 of a normally conducting electron discharge device MI and at some value less than its maximum negative drives it to cut-oft. At cut-off the current flowing to the anode at through the inductance 42 and resistance 53 is interrupted and a transient voltage is induced in the inductance and is applied through a condenser M to the grid 45 of an electron discharge device Mi, driving the device to saturation. The grid 45 has a negative bias, from its connection to the source of bias potential through an inductance 8 and resistance 49, which normally holds the device 4 6 at cut-off.

The voltage at the grid 45, shown at 41, rises abruptly to a peak limited by the grid current in the device 46 and lasts until the stored energy in the inductance 42 is dissipated in the grid 45 and the associated circuits. As the voltage drops, the voltage 37 becomes sufliciently positive to make the device 40 conducting and any negative transient is damped by the flow of current to the anode 4i.

The duration or width of the pulse 47 is determined by the inductance 42, the negative bias on the grid 45, and the magnitude and duration of the voltage applied to the grid 39 and could be changed by varying any of these factors. In the present circuit, the inductance 42 and the bias on the grid 45 are fixed so the pulse width is varied by the tap 38. As the tap 38 is moved toward the upper end of the resistance 36, the

3 rate at which the device 4.0 is driven to cut-ofi' increases, the amplitude of the transient voltage due to the energy stored in the inductance 42 increases, and the device 40 is held longer at cut-01f. All of these factors tend to widen the pulse. Variations in pulse width of from 4 or 5 to 1 have been obtained.

The device 46 converts the positive pulse 4'! to a negative pulse 50 at a terminal 5| connected to the anode 52 and through an inductance 53 to the power supply and to ground through a resistance 14 and a condenser 15. Prior to the pulse 41, no current flows through the inductance 53 and the voltage at the terminal 5| is equal to the voltage of the power supply. At the pulse 41, the device 46 is driven to saturation connecting the terminal 5| to ground through the low impedance of the device. This results in a sudden decrease in voltage at the terminal 5|. With a power supply voltage of 1,000 volts, theterminal voltage may drop to 100 volts, producing a negative pulse of 900 volts. At the end of the pulse 41, the device 46 is driven to cut-ofi and the voltage at the terminal riSes above the power supply voltage due to the induced voltage in-the inductance 53.

While I have shown particular embodiments of my invention, it will be understood that many modifications may be made without departing from the spirit thereof, and I contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope out my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A pulse generating circuit comprising a first, normally conductive, discharge device having an input circuit and having a substantially aperiodic output circuit including an inductive reactance, a source of triggering voltage pulses of peaked waveform, means for impressing a negative triggering pulse from said source on said input circuit, said pulse having sufficient amplitude to drive said device beyond cutofl, thereby to induce a positive voltage pulse of steep wave front and predetermined duration across said 4 reactance, a second, normally non-conductive, discharge device having a substantially aperiodic grid circuit and a load circuit, and means to impress said induced pulse on said grid circuit, 5 said induced pulse having sufiicient amplitude to drive said second device abruptly beyond saturation, said aperiodic circuits being damped for undesired negative transients by return of said first device to conductive condition at the termination of said induced pulse, and means to vary the duration of said induced pulse} m prising means to vary the amplitude of thet gering pulse applied to said input circuit.

2. A pulse generating circuit comprising a first, normally conductive, discharge device having an, input circuit and having a substantially aperiodic ouput circuit including an inductive reactance, a source of triggering voltage pulses of peaked Waveform, means for impressing a negative triggering pulse from said source on said input circuit, said pulse having sufficient amplitude to drive said device beyond cutoff, thereby to induce a positive voltage pulse of steep Wave front and predetermined duration across said reactance, a second, normally nonconductive, discharge device having a substantially aperiodic grid circuit and a, load circuit, and means to impress said induced pulse on said grid circuit, said induced pulse having sufficient amplitude to drive said second device abruptly beyond saturation. said aperiodic circuits being damped for undesired negative transients by return of said first device to conductive condition at the termination of said induced 35 pulse.

RICHARD C. JENSEN.

REFERENCES CI'TED The following references are of record in the 40 file of this patent:

UNITED STATES PATENTS Number Name Date 2,153,202 Nichols Apr. 4, 1939 2,266,668 'I'ubbs Dec. 16, 1941 2,408,061 Grieg Sept. 24, 1946 

